QGIS – Troubleshooting Problems with Animating Heatmap in QGIS Temporal Controller

heat mapqgistemporal-controller

(QGIS 3.20) I am having trouble getting my heatmap to animate properly using temporal controller. I am using a point layer with many points in the same location so a heatmap would really help visualize the data. But, when using temporal controller, every year shows exactly the same image.
These are the temporal settings I'm using:

I have the same layer symbolized as points, with exactly the same temporal settings – this layer animates fine and shows the changes from year to year. So I don't think the problem is with these settings, but I could be wrong.

I generated the heatmap layer by duplicating the point layer and changing the symbology to Heatmap.

What am I doing wrong?

Best Answer

Solved, there were a couple issues going on:

Null date values were showing up in every frame and needed to be filtered out
The radius in heatmap symbology was too large, preventing me from seeing the very small changes.
I played around with the "maximum" option in heatmap symbology to better seperate different densities.

Solution

The trick is to use a date somewhere in the middle of the year, not at the beginning of the year and to set an event duration of less then a year in the layer property settings.

How to make settings

From your date, create a new field date2 by adding 6 months: "date" + to_interval ('6 months')
In the Layer Properties / Temporal Tab set Field to date2 and for Event duration set something like 30 days.
In the temporal controller interface, be sure to set Animation range from start to end of a year (like 1933-01-01 to 1955-12-31) and Step to 1 year.

Explanation

Now only if end of June is included in the current frame's range, the relevant features will show on the map. So even if the time range of the current frame "shifts" in a way that it overlaps the divide between two years (like 1937-01-01 06:00:00 to 1938-01-01 06:00:00), only 1937 will show up as 1937-06-30 is within this range, but not 1938-06-30. If you had 1938-01-01, however, both would show.

QGIS Temporal Controller – Get Current Animation Time with Expressions/Variables

You can get the percentage by using an expression such as:

second(datetime_from_epoch(epoch(to_datetime(to_string("mytime")+'Z')) - epoch(@animation_start_time)) - make_datetime(1970,1,1,0,0,0)) / second(@animation_interval)

Be aware of the timezones! Seems like QGIS temporal-controller-variables always work with UTC, while your datetime may be in another timezone. You can correct this by adding or subtracting the hour difference in seconds. Or a little more elegant change the 0-time of make_datetime(1970,1,1,0,0,0) to e.g. make_datetime(1970,1,1,1,0,0) In my example above I had to manually set UTC as timezone, thats why I use to_string("mytime")+'Z'. Remove that part if you dont need it!

Example result:

Best Answer

Related Solutions

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How to make settings

Explanation

QGIS Temporal Controller – Get Current Animation Time with Expressions/Variables

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